Hippopotamus

SCIENTIFIC NAME: Hippopotamus amphibius

SWAHILI NAME:
Kiboko

Few animals are as recognizable as the hippopotamus, with its soap-bar-shaped body; great, yawning mouth; and tiny, mobile ears. These enormous herbivores are native only to Africa. Their bodies are engineered to adapt to a mostly aquatic lifestyle. A hippo’s nostrils are on the top of its snout and zip themselves shut as soon they encounter water, and its skin acts like a dive suit to keep the hippo warm underwater and cool on land.

Size

Tracks and Scat

Tracks: Flat center with four deep toe marks; same-size front and hind tracks; best seen on paths leading to and from rivers
Scat: Similar to elephant's, but hippos scatter dung widely with their tails; often defecate in water

Trivia Question

How much of a hippo’s body weight does its skin comprise?

18 percent

12 percent

8 percent

Correct!

Incorrect!

A hippo’s skin is one of its most important organs. It’s incredibly sensitive and strong, and can be up to 2.4 inches (60 mm) thick. It represents 18 percent of its body weight!

Social Structure

Hippos have a loose, relaxed social structure. During the day, they rest in large pods made up of both sexes of various ages. Group size depends on the desirability of the habitat. Hippos prefer water that is slow-moving and deep enough to cover their bodies—5- to 6-feet (1.5- to 2.0-m) deep—along sandy, open shorelines. Preferable habitat can host gatherings of more than 200 hippos. Solitary hippos tend to be females getting ready to give birth or elderly males. Otherwise, hippos gather either in nursery schools—females and their calves—or bachelor groups. These rules are loose, though, and members of any sex or age may turn up in a group. These groups break up for evening grazing. Some adult bulls defend territories where they are the most dominant member. Dominance is loosely based on size. Bulls mark and defend their territories with urine and feces, which they fling impressive distances by waggling their tails. When a male enters another male’s territory, he becomes submissive to that male unless he intends to challenge him. When males fight for a territory, they rake their teeth along each other’s flanks. Despite their thick skin, these fights can lead to serious injury or even death.

Communication

Hippos use sound and body language to communicate. They honk—both on land and in the water. These honking calls can be nearly 115 decibels (the volume of loud thunder) and can be heard a mile (1.6 km) away. Hippos also make various noises underwater—grunts, squeaks, croaks, and whines—though the meaning of all these sounds is not understood. The most famous method of hippo communication is opening their mouths in impressively wide “yawns.” One possible explanation for this behavior is that it signals excitement.

Behavior

Despite their aquatic tendencies, hippos cannot actually swim or float. Instead, they walk along the bottom of rivers and watering holes. When completely submerged, they push off from the bottom to get back to the surface. Hippos spend most of the day in and out of the water. When they get cold, they move to the banks and bask in the sun; when the sun gets too hot, they return to the water to cool down and get out of the sun. Most of the night, they graze on dry land. They tend to return to the same resting places every day. In swampy areas, the channels and trails hippos make may alter the flow of water. When moving at full tilt, hippos can reach speeds of almost 20 miles an hour (30 kph).

Conservation

Hippos live all across Africa—many in protected areas—but their populations are decreasing due to drought, poaching, habitat loss, habitat fragmentation, and the damming of rivers. They are poached not only for their meat but also for their teeth. Called “ivory,” they allegedly are softer and easier to carve than elephant tusks. Hippos are also vulnerable to rinderpest, a communicable cattle disease, as well as anthrax, which is capable of killing hundreds or even thousands of hippos within an infected area. The International Union for Conservation of Nature (IUCN) lists them as a vulnerable species.

Range & Habitat

Hippos live in grasslands and bushlands throughout sub-Saharan Africa, although several centuries ago, they ranged as far as the Nile Delta.

Hippos need a permanent water source and sufficient grass to survive. Water helps these animals regulate their body temperature and protects them from scalding sunburns, so they never wander far from a water hole, lake, river, or swamp.

Diet

Aquatic plants are typically rare in hippo habitat, so terrestrial grass makes up most of a hippo’s diet, though in some areas, bushes, water lilies, and other plants make up as much as 15 percent of what they eat. They pull up plants with their strong lips rather than with their teeth. On very rare occasions, hippos have been spotted killing and eating wildebeest and antelopes such as impalas, or scavenging the corpses of other hippos.

Breeding

Mating occurs during the dry season and usually takes place in the water. Females breed with territorial males and may visit two or more different territories over the course of their two- to three-day estrus period. After a 240-day gestation, a mother gives birth in the water to a (relatively) tiny calf, weighing between 50 and 110 pounds (25 to 45 kg). For about ten days, the calf and its mother are solitary and stay close to the water’s edge. The mother will attack any other hippo, including a territorial male, that approaches. After this bonding period, the mother begins to graze on the bank during the day. When the calf is a few weeks old, it begins to go with its mother to the grazing grounds at night. There, the calf hides under a bush while she eats. Weaning occurs when the calf is about six or eight months old. Females give birth to calves about once every two or three years. Calves and their mothers remain close even after the birth of younger siblings. Scientists have seen mothers with as many as three calves of various ages trailing behind them. The youngest calf is always closest to the mother, while the eldest brings up the rear. Both males and females typically become sexually mature at around seven years of age, though females occasionally mature much earlier.

Friends & Foes

Hippo poop adds terrestrial nutrients to lakes and rivers. It likely acts as fertilizer and may be an important food source for aquatic animals, such as fish. Many birds, including oxpeckers, like to perch on hippos’ backs and hunt for ticks and other insects. Many African fish “clean” hippos by plucking loose skin, parasites, and debris from them, even swimming into their mouths. Hippos also have been observed rescuing antelopes from drowning by pushing them up onto banks and intervening to save them from crocodiles. Ambitious prides of lions occasionally hunt and kill a hippo, and a crocodile may sometimes eat a hippo calf, but grown hippos seem unfazed by crocodiles. Although hippos have a reputation for being one of the deadliest animals for humans in Africa, humans and hippos typically coexist peacefully unless crops are involved. Hippos are inveterate crop raiders and are only slightly discouraged by chain-link or electric fences. Hippos can attack—and often kill—humans who encroach on their resting areas during the day or who get between mothers and calves on land at night.

Population in Kenya & Beyond

Hippos are difficult to count accurately because they spend a significant proportion of their time underwater, don’t surface in synchrony, and come ashore mainly at night. However, scientists estimate that there are between 125,000 and 148,000 of these animals in the wild, with the majority living in East Africa. Kenya alone has about 5,000 of them, and a pod of about 25 inhabits Mpala’s hippo pool.

Did you know?

The skin of hippos secretes a reddish substance that may act as a kind of sunscreen and helps cuts heal quickly.